Actinium Pharmaceuticals, Inc. highlighted data from multiple abstracts that were presented at the 2024 Society of Nuclear Medicine & Molecular Imaging (SNMMI) Annual Meeting being held June 8 ? 11, 2024, in Toronto, Canada. The presentations featured results from the Phase 3 SIERRA trial of Iomab-B, a CD45 targeting ARC with the Iodine-131 payload, intended for conditioning to prepare patients with active relapsed or refractory acute myeloid leukemia (r/r AML) for a potentially curative bone marrow transplant (BMT).

The Phase 3 SIERRA trial enrolled 153 r/r AML patients. Iomab-B achieved the primary endpoint of durable Complete Remission (dCR) with high statistical significance (p<0.0001). Additionally, Actinium's novel linker technology was highlighted in a presentation demonstrating high tumor uptake and in vivo stability in preclinical models with significantly lower kidney and liver uptake compared to standard DOTA linkers.

Survival Outcomes and Dosimetric Analysis of Iomab-B (131I-apamistamab) Followed by Allogeneic Hematopoietic Cell Transplant for Patients with TP53 Mutated Relapsed/Refractory AML. 37 patients (24%) enrolled on SIERRA had a TP53 mutation with 27 patients receiving Iomab-B (either through randomization or cross over) and 10 patients on the control arm. For patients with TP53 mutation who received Iomab-B, the median OS was 5.49 months compared to a median 1.66 months in pts who did not receive Iomab-B (HR=0.23; 95% CI [0.10, 0.52]) .

These results support Iomab-B's differentiated mechanism of action to overcome the negative impact of TP53 mutation typically associated with a dismal prognosis in these patients. Exploratory Analysis of Bone Marrow Dosimetry from the Randomized Phase 3 SIERRA Trial of Iomab-B (131I-apamistamab) Prior to HCT in Relapsed/Refractory Acute Myeloid Leukemia. Iomab-B safely delivers high doses of myeloablative targeted radiation to the diseased bone marrow at greater amounts than what would be achieved with total body irradiation.

Myeloablative doses were safely delivered to patients irrespective of age, performance status and other metrics. A median of 16Gy of radiation was delivered to the bone marrow while normal healthy organs received significantly less exposure, including the heart (2.6 Gy), lungs (2.5 Gy), small intestine (2.4 Gy), stomach (3.6 Gy), kidneys (4.1 Gy) and the whole body (3.3 Gy). Mathematical Modeling of Exposure Measurements Following High-Dose Targeted Therapy Using 131I-apamistamab: Analysis From the Large Multicenter Phase III SIERRA Trial.

SIERRA patients received up to 1,030 mCi (range: 300-1,030) of Iodine-131 via Iomab-B, Iomab-B is administered via a single infusion 12 days prior to BMT, Data from SIERRA show that the median time for patients to reach the release criteria was 5 days, including in patients receiving greater than 800 mCi. Evaluation of novel DOTA-based linkers for improved targeted radiotherapy delivery to solid tumors. Novel linkers showed significantly lower kidney and liver uptake compared to standard DOTA linkers, SPECT/CT imaging showed high tumor uptake and in vivo stability in preclinical models, Successful design, efficient conjugation and pharmacological properties support further advancement of these novel linkers.

Actinium has two wholly owned U.S. patents covering its novel bifunctional linker technology with each having a patent term extending into 2043 and a pending international patent application.